In the web printing process, the ink is applied to the paper and typically passed through an oven to cure. However, the ink printed on the paper web is often not sufficiently cured after it exits a drying oven. Because of the incomplete cure, the printed ink can be marred, or smeared, by abrasion against the rollers, former board, cutters and folders. Further, the paper can often obtain a static charge buildup during the printing which in turn can often cause problems such as paper jams or poor stacking on the pallet at the end of the line.
It is known in the art to apply silicone standard emulsions (emulsions having a particle size of greater than 300 nanometers) to the paper web immediately after the cure to act as an antimarring agent. Commercial fabric softeners are often added to the silicone standard emulsion bath to act as antistatic agents. The emulsion is applied to the printed paper by contacting the paper with a roller which is continuously coated with the emulsion. The ability of the emulsion to spread evenly over the surface of the roller from which it is applied is known as wettability or wetting. Silicone standard emulsions often lack good wetting onto the applicator roll which results in spotty and incomplete application of the emulsion onto the paper.
Further, the standard emulsions are not stable when diluted to low levels and/or they may lose their effectiveness when diluted to low levels. Typically, the printers purchase the standard emulsions in a "concentrated" form and dilute the standard emulsion to the desired concentration prior to use. However, the web printers may end up using the standard emulsion in higher concentrations than actually necessary due to instability at lower concentrations. This leads to waste of the standard emulsion and increased production costs.
There has been a long felt need in the web printing industry for improved silicone emulsions with higher efficiency in antimarring and a higher antistatic agent content. It is also preferred that the antistatic agent be contained in the emulsion to eliminate the need for adding costly commercial fabric softeners. However, with the silicone standard emulsions, increasing the cationic surfactant to improve the antistatic properties decreases the wettability and can also decrease dilution stability. Adding a nonionic surfactant or using higher amounts of nonionic surfactant can correct for the decrease in wettability but will cause particle flocculation which degrades the emulsion stability. Further, with silicone standard emulsions known in the art, there are limits on the amount of surfactants that can be added without degrading the emulsion. Often these limits are insufficient and do not result in an increase in the performance of the emulsion in reducing the marring and static problems.
U.S. Pat. No. 4,637,341 to Switall teaches the use of silicone emulsions in web paper printing. The invention described in U.S. Pat. No. 4,637,341 mostly pertains to an apparatus for applying an aqueous silicone emulsion to the paper web as it is moving through the printing press. The apparatus taught by Switall provides an on-line means of diluting the concentrated silicone emulsions for use in the web printing process. Switall does not provide any details on the type of silicone emulsions useful or improvement made to antimarring or antistatic properties from the process taught therein.
U.S. Pat. No. 4,551,385 to Robbart teaches the use of reactive siloxanes which are chemically bonded to cellulosic materials to improve printing characteristics. The reactive siloxanes are applied to the cellulosic material and cured prior to the printing with ink.